sedimentary

Chert Nodule

Microcrystalline Quartz (SiO2)

Hardness: 7 (Mohs scale), Color: Cream to yellowish-tan, Luster: Waxy to dull, Crystal Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture)

Identified July 21, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale), Color: Cream to yellowish-tan, Luster: Waxy to dull, Crystal Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture)

Formation & geological history

Formed in sedimentary environments through the chemical precipitation of silica or the replacement of carbonate minerals by silica-rich fluids. Often found embedded in limestone or chalk beds.

Uses & applications

Historically used for making stone tools (flintknapping); commercially used in construction aggregates and occasionally for lapidary work.

Geological facts

Chert is essentially the same mineral as flint, but the term 'flint' is usually reserved for dark grey/black varieties found in chalk. It is highly resistant to weathering.

Field identification & locations

Identify by its hardness (cannot be scratched by a steel nail) and characteristic curved (conchoidal) fractures where it has broken. Commonly found in riverbeds or eroded out of limestone cliffs.